FIG. 13 is a block diagram showing a transport stream (described as TS herein after) multiplexing transmission device for multiplexing and transmitting information as a transport stream which is an example of a multiplexed bit stream disclosed in, for instance, "Image and information engineering and broadcasting technology" issued by Institute of Television Engineers of Japan, Vol. 49, No. 4, (Whole Number 560), special number MPEG "3-4 system" (April, 1995 number thereof).
In FIG. 13, designated at the reference numeral 1 is a clock generating section, at 2 a video coding section, at 3 an aural coding section, at 4 a information coding section, at 5 a program-specific information generating section, at 6 a media multiplexing section, at 7a, 7b . . . 7n a program generating section respectively, at 8 an all program control information generating section, and at 9 a program multiplexing section.
Next description is made for a method of generating a program-a in the program generating section 7a of the TS multiplexing transmission device as operations of an example thereof based on the conventional technology. A video signal 102, an aural signal 103, various information signals 104 are coded as a information source in the video coding section 2, the aural coding section 3, and the information coding section 4 respectively, so that video coded information 106, aural coded information 107, information coded information 108 can be obtained. The inputted coded information is contained in packets which are multiplexed as a bit stream by the media multiplexing section 6.
Description is made herein for a transport stream packet (described as a TS packet hereinafter) with a fixed length comprising 188 bytes as an example of packetizing. FIG. 14 shows configuration of a TS packet, in the figure, designated at the reference numeral at 113 is a packet header with a 4-byte length, at 114 a packet ID number (described as a PID number hereinafter), and at 115 packet information with a 184-byte length. The video coded information 106, aural coded information 107, and information coded information 108 each coded according to the information source are putted into packet information 115 of the TS packet which has different PID numbers 114 respectively. As an example herein, it is assumed that the video coded information 106 is transmitted with a packet having a PID number of PID-aV, the aural coded information 107 with a packet having a PID number of PID-aA, and the information coded information 108 with a packet having a PID number of PID-aD. On the other hand, the coded information in the packet information 115 is identified as each of media types according to the PID numbers 114 in the packet header 113 in the receiving side.
On the other hand, the clock generating section 1 generates, for instance, as a system clock source, a 27-MHz system clock from a 13.5-MHz clock signal 101 used for sampling of a video signal 102, and outputs clock information 105 for the generated clock at a specified time interval. The clock information 105 is putted in the TS packet in the media multiplexing section 6 for transmission, and is used for regeneration of the clock in the receiving side. Herein, it is assumed that clock information 105 is transmitted with a packet having a PID number of PD-aC. Detailed description will be made later for a clock regenerating method using this clock information 105.
In the program-specific control information generating section 5, program-specific control information 109 shown in FIG. 15 is generated. In the information, PID numbers of a packet each used for transmitting the video coded information 106, the aural coded information 107, the information coded information 108 and the clock information 105, media types to each of the coded information, and a coding system are described as information for packet ID numbers. This program-specific control information 109 is also designated as a program map table (PMT).
The media multiplexing section 6 generates TS packets having PID numbers corresponding to inputted video coded information 106, aural coded information 107, and information coded information 108 respectively, and in addition, by containing the program-specific control information 109 in a TS packet, the media multiplexing section 6 generates a program-specific control information packet with a PID number of PID-aM. In this case, the clock information 105 generated by the clock generating section 1 is included in the packet with a PID number of PID-aC. Finally, the media multiplexing section 6 multiplies all the packets for the generated video/audio/information/program-specific control information, and generates a packet of program information 110a for the program-a. Similarly, each of the program generating sections 7b to 7n generates each program information 110b, . . . , 110n for each program.
All program control information 111 as shown in FIG. 16 is generated by the all program control information generating section 8. Information for all programs contained in program multiplexed information 112 is written in the all program control information 111, and, for instance, a number of programs, all titles of the program, a PID number of each of the program-specific control information packets, and view ability restricting information or the like are included therein. PID-aM, PID-bM, . . . , PID-nM as PID numbers of program-specific control information packets for the programs a, b, . . . , n are written in the example shown in FIG. 16. This all program control information 111 is also called as Program Association Table (PAT).
Then, the program multiplexing section 9 packetizes the all program control information 111 generated by the all program control information generating section 8 to generate an all program control information packet with PID-P (e.g. 0.times.00) as a prespecified PID number, multiplexes the generated packet with the TS packets for the program information 110a, 110b, . . . , 110n generated by the program generating sections 7a, 7b, . . . , 7n, and outputs the multiplexed packets as the program multiplexed information 112. In a case where a information generating speed for information to be transmitted (in this case, the program information 110a, 110b, . . . , 110n and all program control information 111) is slower than an output rate (speed) of the program multiplexed information 112 specified at a speed in the transmission path, a null packet (packet information 115 in a TS packet is dummy information) is inserted into the program multiplexed information to match the processing speed by the program multiplexing section 9.
Description is made for operations of a TS receiver for receiving the program multiplexed information 112 transmitted from the TS multiplexing transmission device and regenerating the received information in accordance with the flow of a media regenerating processing shown in FIG. 17.
The TS receiver, when starting to receive program multiplexed information 112 after starting up, at first, fetches thereinto a packet with the prespecified PID number of PID-P, and obtains all program control information.
Then, it is known that programs a, b, . . . , n are contained in the program multiplexed information 112 according to the obtained all program control information. Herein, in a case where the program-a is selected, it is known that program-specific control information therefor is contained in a packet with PID-aM. The receiver fetches thereinto the packet with the PID number of PID-aM, and obtains PID numbers, corresponding to the packets in which the media (video, voice, information) each constituting the program-a and clock information required for media regenerating processing are contained, from the program-specific control information for the program-a. The receiver regenerates each of the media information by receiving each of the packets with the obtained PID numbers.
Herein, description is made for a method of synchronizing frequencies of operating clocks (system clocks) in the transmitting side as well as in the receiving side with the clock information 105 with reference to FIG. 18.
In FIG. 18, in a case where a system clock is generated, for instance, with respect to the video signal 102, the video coding section 2 fetches a 13.5-MHz clock used when the video signal 102 is subjected to sampling as a clock signal 101, and from this signal, a 27-MHz system clock is generated by a PLL 13 (Phase Locked Loop) incorporated in the clock generating section 1. A counter value of a counter 14 for counting the system clock is transmitted to the receiving side at a specified cycle (e.g. once in 100 milliseconds) as clock information 105.
Clock information 116 for a program to be generated is separated from the received program multiplexed information 112 in a separating section 16 of the TS receiver 12. When receiving is started, a value of the separated clock information 116 is set in the counter 14 of the clock generating section 17, and the 27 MHz system clock is operated in the PLL 13 for counting up the counter 14. Then, the received and separated value of the clock information 116 is compared to the counter 14 by a comparator 18, a difference is given to the PLL 13, and the frequency of the system clock is corrected according to the difference. After the step and on, the same comparison and correction as those described above are executed to received and separated clock information 116, so that, by decoding coded information with the system clock 7 in the transmitting side, accurate video signals and aural signals can be regenerated. It should be noted that, in a case where fluctuation is generated in transmission of the clock information during the transmission thereof, turbulence is generated in the regeneration of the system clock in the receiving side, and an overflow or an underflow is generated in the buffer of the decoder because of inconsistency between the frequency of the system clock in the transmitting side and that in the receiving side. As a result, turbulence is generated in a received video and a sound or the like.
By the way, in the latest community antenna television system or the like, the TS multiplexing transmission device as already described above multiplexes a plurality of programs and transmits the multiplexed programs. In a case where a viewer subscribes to a plurality of broadcasters as described above, at first, the viewer selects one of the broadcasters, and then selects a program that the viewer wants to look at out of the plurality of programs broadcasted from the broadcaster according to the flow shown in FIG. 17.
FIG. 19 is an example showing the broadcasting system, and there is shown herein a case where the TS multiplexing transmission devices 10a, 10b, . . . , 10n described above are provided in each of the broadcasters, and each of the viewers has the TS receiver 12 provided therein and views a program thereby. As for the TS receiver 12, one out of the TS multiplexing transmission devices 10a, 10b, . . . , 10n provided in the broadcasters to which the viewer subscribes is selected by the receive selecting section 11, and a line is connected thereto with a method specified in a transmission path (e.g. a satellite or a ground wave, a coaxial cable, and an optical fiber or the like) between the TS receiver and the selected TS multiplexing transmission device. Then, all program control information, program-specific control information, and media information are obtained from the bit stream transmitted through the selected line and each of the obtained information is regenerated.
The transport stream multiplexing transmission device based on the conventional technology has the functional configuration described above, so that, in the TS receiver, a plurality of transport stream multiplexing transmission devices, namely transport stream cannot simultaneously be obtained from a plurality of broadcasters.
Only by remultiplexing transport streams from the plurality of transport stream multiplexing transmission devices simply into one transport stream for transmission, ID numbers of packets each containing all program control information have the same values in all the transport streams, which makes it impossible to identify which transport stream multiplexing transmission device the transport stream corresponding to one unit of all program control information is sent from.
Even if all program control information contained in transport streams sent from the plurality of transport stream multiplexing transmission devices are taken out therefrom to generate new all program control information, media information can not be obtained because the packet ID number for the media information contained in these transport streams may sometimes be the same as that for others.
The transport stream which has a small amount of capacity of program information and is transmitted by inserting a null packet to match the processing speed is low in transmission efficiency, so that the transmission path can not effectively be utilized.
In a case, for instance, where a plurality of transport streams transmitted through a transmission path with a low speed are remultiplexed into one transport stream and is transmitted through a transmission path with a high speed, it is difficult to match the speed therebetween.
A transport stream from a transport stream multiplexing transmission devices comprises a plurality of programs, so that there is a case where an unnecessary program is also transmitted.
A transport stream from a transport stream multiplexing transmission devices comprises a plurality of programs, so that there is a case where all-ages programs and programs for adult people are mixed therein, and for this reason viewability restriction has to be set in each program.
A transmission delay of packets is sometimes generated due to remultiplication of a plurality of transport streams, so that program clock information contained in the transport stream can not accurately be transmitted, and for this reason, the clock can not accurately be regenerated in the receiving side.
Transmission of each of transport streams from the plurality of transport stream multiplexing transmission devices is discretely executed respectively, so that one of transport streams is not synchronized to others, and for this reason, it is difficult to obtain synchronism between inputted transport streams when packets are remultiplexed.
The conventional type of transport stream multiplexing transmission device has only a function of packetizing media information therein for transmission, so that the device can not fetch the transport stream already multiplexed as input information thereinto, for remultiplexing the information generated in the devices together with media information packets for transmission.